The term “airfoil” broadly describes several species of elongate machined parts, such as blades, vanes and nozzles. The wake profile of an airfoil includes data related to flow angle and total pressure. In airfoil testing, the wake profile of an airfoil is determined by traversing a probe in a circumferential direction blade to blade at various radial locations. The probe moves continuously in the circumferential direction while three pressures from three holes and information indicating probe location are simultaneously recorded.
All known commercially available 3-hole probes measure flow angle and total pressure using three sensor holes aligned perpendicular to the probe axis. See FIGS. 1 and 2. Such probes can be used to determine flow direction, i.e., a yaw angle, based on the pressure difference between the outermost holes.
In turbomachinery testing, such probes are usually inserted into the test location radially. Since the trailing edge of the airfoil is also radially-extending, or very nearly so, the probe holes are aligned perpendicularly to the trailing edges. Probes oriented in this manner cannot measure airfoil wakes accurately because the pressure gradient of the wake is very large. A large pressure gradient across the probe width results in a single hole being located in the wake while the other two holes are located outside of the wake, that leaves erroneous flow direction information.